1. Field of the Invention
Embodiments of the invention generally relate to electronics, and in particular, to voltage-controlled oscillators.
2. Description of the Related Technology
Voltage-controlled oscillators (including digitally-controlled oscillators) are widely used in electronic and communication applications, such as clock generation and distribution, carrier synthesis, and data-recovery. Voltage-controlled oscillators can include an oscillator core that generates an oscillating output signal and a resonator or LC tank that presents the oscillator core an electrical characteristic such a capacitance and inductance that causes the oscillatory response. The frequency of oscillation depends at least partly on the value of the electrical characteristics. Accordingly, voltage-controlled oscillators have LC tanks with variable electrical characteristics, thereby providing a way to control the frequency of oscillation of the output signal by adjusting or tuning the variable electrical characteristics.
Push-push oscillators are used in many applications due to their tunable bandwidth, low noise, and low frequency pulling. Push-push oscillators may also increase tuning frequency by a factor of two. Such an oscillator represents a balanced circuit, in which two bipolar junction transistors (BJTs) provide opposite phase oscillations at the fundamental frequency and odd harmonics and in-phase oscillations at even harmonics. Push-push oscillators can be coupled with a diode-based varactor for tuning of the frequency of oscillations.